Mayer is notorious for being not very interested in the advertising business, which is so central to Yahoo's future.

De Castro, meanwhile, is known as someone who is exceptionally bright and hard-working, but sometimes awkward with people.

The agency source we talked to asked not to be named so that he or she could be candid in his or her response.

The short answer from this person is that there is much optimism around Yahoo because it has hired Marissa Mayer, a rock star tech executive, but that she and De Castro need to do a much better job filling their agency partners in about their plans going forward.

"It's a very fuzzy vision that they've put forward."

This source also warns Mayer and De Castro that it may seem like Yahoo can win without the help of agencies, but that "the road is littered with corpses of technology companies thinking they can disintermediate agencies or ignore them"

He says that there is one big trick Mayer needs to figure out if Yahoo is going to start growing revenues again.

"When you have a productive and fruitful relationship between an agency and an audience provider like Yahoo, Google, or Facebook, you can grease the skids and see the revenue follow."

"My hope is that Yahoo figures this out sooner rather than later. But right now that's a fuzzy black box."

Here is a lightly edited transcript of this source's complete thoughts.

On the agency community's hopes for Yahoo:

The overall sentiment at the agencies is that there is a hope and optimism that Yahoo's new leadership is going to get some stability and really emerge as the force we need it to be.

They're an important player — an important aggregator of quality audience.

The agency world wants to see Yahoo be successful. It is extraordinarily difficult to find a replacement for the aggregated attention and quality of consumers Yahoo brings today.

If Yahoo were to shut up tomorrow it would make business incrementally harder. In our game scale matters materially.

Right now, Yahoo is an ecosystem that's not as good as it ought to be or as it should be, but by no means does it suck.

There is no one in the agency community who says Yahoo sucks.

On Mayer's vision for Yahoo:

There are companies that aggregate user attention around functionality and productivity, like search and storage, and there are companies that aggregate user attention around content experiences.

They need to pick one of these two.

I don't think Yahoo is really clear on that position.

On the one hand, Henrique says the modern portal experience delivers personalization of content. That's great. Fine. But I don't see how that's consistent with Marissa's vision to build a company that reinvents email and search.

I'm not saying the consumer experience isn't important, but Yahoo has to focus on what they're going to deliver to whom.

On Mayer's "lack of connection and responsiveness" to agencies:

It's a very fuzzy vision that Mayer and De Castro have put forward. I'm not saying that it's right or wrong, at the moment it's still a little abstract.

I sense there is frustration on the agency side about lack of connection and responsiveness to the agency community.

I think it's a big mistake.

It's not a job you need to outsource to anyone else.

The agency community spends billions of dollars. If you've got that concentration of spend, you want to have a very favorable relationship with those folks.

For the community, that's why everyone was so bullish on [former Yahoo interim CEO] Ross [Levinsohn]. He understands what agencies are trying to accomplish with brands.

The road is littered with corpses of technology companies thinking they can disintermediate agencies or ignore them. Every company has gone through that cycle. First they say "screw the agencies, we're going to go to clients alone" — only for them to come back six months later. That's what Yahoo did. That's what Facebook did until Carolyn Everson came along. That's what Google did until Tim Armstrong brought up the agency team.

I think Yahoo has so many CEOs in such a short period of team, the institutional sales force has been kind of decimated so maybe they have to go through that process again before they can come to terms and move forward.

A lot of people from the outside look at it and say that agencies are dumb and we can do this better ourselves. In many ways they are correct.

But with global media agencies, you have one group of people who manage multiple investments across multiple channels.

Tomorrow someone is going to come up with something that will reach consumers and vie for the spend of our clients.

There's no evidence that Fortune 500s are abandoning agencies that manage their investment.

What does happen is when you have a productive and fruitful relationship between an agency and an audience provider like Yahoo, Google, or Facebook, you can grease the skids and you see the revenue follow.

My hope is that Yahoo figures this out sooner rather than later. But right now that's a fuzzy black box.